Continuous slab casting is a steel making process where molten (liquid) steel from a ladle is continuously cast into cast metal strand of a semi-finished shape (e.g., slabs, blooms, and billets). In a continuous slab caster, the molten metal is fed by gravity from the ladle through a tundish to a subentry nozzle (SEN) in a casting mold. The semi-finished shape is determined by the casting mold which receives the molten steel through the SEN. The steel is cast in the casting mold, which is water cooled, with a solidified outer shell and molten inner core as the strand moves downwardly through the mold which oscillates. The cast metal strand is withdrawn downwardly from the casting mold and is curved by casting guide rollers and straighteners to exit the casting machine laterally in a horizontal direction of travel. The strand is further subjected to secondary cooling upon exiting from the casting machine by direct and/or secondary cooling to solidified the core of the strand. The strand is then cut to length into slabs, blooms, or billets.
In the continuous caster, the SEN discharges the molten metal into the mold at a selected depth below the surface (the meniscus) of the melt in the casting mold. The flow of the molten melt from the tundish is fed by the ferrostatic pressure difference between the liquid levels in the tundish and that of the melt in the casting mold. The melt flow from the tundish may be controlled by a stopper rod, which at least partially blocks the exit port to a shroud leading to the SEN, or a slide gate that moves across the outlet port of the tundish to the shroud. As the molten metal enters the mold, the steel solidifies at the water cooled mold walls to form an outer shell, which is continuously withdrawn at the casting speed to produce the steel strand by oscillation of the mold walls. The rate of formation of the cast metal strand by the casting machine is substantially equal to the rate of flow of the molten steel through the SEN into the casting mold.
The width of the steel strand exiting the mold is determined substantially by the relative separation and taper angle of opposing faces of the casting mold. The molten steel tends to shrink in the mold (i.e., pull away from the mold faces) as it cools and moves from the top of the mold (e.g., adjacent the SEN) to the bottom of the mold. The mold faces are tapered to account for the shrinkage, so that the molten steel moving through the mold may maintain contact with the mold faces.
As the strand exits downwardly from the casting mold, the strand enters containment segments which serve to further cool and solidify the strand. The rolls of containment segments may also apply pressure to the strand to reduce the thickness of the strand. As the strand exits the containment segments, the strand may enter a set of pinch rolls which serve to feed the hot metal strand downward from the mold and toward a withdrawal straightener. A disconnect roll positioned below the set of pinch rolls may be provided to initially direct the cast metal strand toward the withdrawal straightener and to disconnect a starter dummy bar from the cast metal strand. The dummy bar allows the start of casting by providing a surface onto which to cast the strand at the start of the cast.
The cast metal strand enters the withdrawal straightener which serves to transition the strand laterally to a horizontal direction of travel. The withdrawal straightener provides support for the hot metal strand as the strand cools and progresses at casting speed through the withdrawal straightener and toward a cutting tool which is external to the withdrawal straightener. The withdrawal straightener includes drives to move the cast metal strand through the withdrawal straightener as casting proceeds.
By the time the cast metal strand exits the withdrawal straightener and enters the cutting tool, the cast metal strand is generally solid and significantly cooled such that the strand is ready to be cut (i.e., transverse to the direction of travel of the strand) to form a cast shape such as slabs, blooms, or billets. The cutting tool may comprise a shear having, for example, cutting blades. For thicker strands, a cutting torch, or other cutting mechanism suitable to cut the cast metal strand laterally may be used. As the strand is cut into slabs, for example, the slabs are generally transported away on rollers to be further processed.
As the cast metal strand travels from the casting mold through the casting machine and beyond to the cutting tool, the strand may tend to wander, distort, and twist due to forces exerted on the strand. Such forces may be due to cooling of the strand, or forces exerted by the pinch rolls or withdrawal straightener. It is desirable to keep the cast metal strand positioned substantially orthogonal to the direction of travel for the casting machine to work effectively and produce quality strands at commercial casting speeds.
Methods are disclosed for continuously casting metal strand and for monitoring and controlling a cast metal strand in a continuous metal slab caster comprising the steps of:                monitoring a first lateral position of a cast metal strand adjacent entry to a withdrawal straightener,        monitoring a second lateral position of the cast metal strand adjacent exit from the withdrawal straightener,        monitoring a third lateral position of the cast metal strand downstream of a cutting tool, and        electronically storing the monitored lateral positions as associated data in a computer-based system and using the associated data to actuate at least one correcting device capable of adjusting the orientation of the strand during casting.        
The methods may further include monitoring an elevation position of the cast metal strand adjacent the withdrawal straightener and optionally adjacent a set of pinch rolls, and electronically storing the monitored elevation position in the computer-based system as a part of the associated data. In an embodiment, monitoring of the elevation position may be accomplished by detecting an elevation location of a first broad side of the metal cast strand. Monitoring of each of the first, second and third lateral positions may also be accomplished by detecting a first lateral location of a first narrow side of the cast metal strand and a second lateral location of a second opposite narrow side of the cast metal strand. The detecting may be accomplished using a laser sensor capable of detecting the monitored elevation position and using pairs of laser sensors capable of detecting the opposite sides of each lateral positions monitored.
The stored associated data is processed by the computer-based system to generate at least one control signal such as, for example, a feed-forward control signal and a feedback control signal. The control signals are used to control one or more correcting devices, such as mold taper of a casting mold, roll force or pressure profile of the rolls of the withdrawal straightener, tilt of the withdrawal straightener, tilt of the set of pinch rolls, cooling sprays operating on rolls adjacent the slab caster, drive speed of the set of pinch rolls, and drive speed of the withdrawal straightener.
Also, a continuous slab caster and a system for a continuous metal slab caster are disclosed comprising:                a first pair of position-detecting sensors positioned laterally with respect to a direction of travel of the cast metal strand adjacent entry to the withdrawal straightener,        a second pair of position-detecting sensors positioned laterally with respect to a direction of travel of the cast metal strand adjacent exit from a withdrawal straightener,        a third pair of position-detecting sensors positioned laterally with respect to a direction of travel of the cast metal strand downstream of a cutting tool, and        a computer-based apparatus electrically connected to the first pair, second pair and third pair of position-detecting sensors and controlling at least one correcting device capable of adjusting the orientation of the strand during casting.        
The slab caster and the system may further comprise a fourth position-detecting sensor positioned to detect the strand substantially orthogonal along a direction of travel of the cast metal strand adjacent the withdrawal straightener and optionally adjacent a set of pinch rolls. If used, the fourth position-detecting sensor is electronically connected to the computer-based apparatus. In an embodiment, the sensors may include laser devices and the computer-based apparatus may include a programmable logic controller (PLC) capable of being programmed with automation software. The computer-based apparatus may be capable of receiving a position signal, corresponding to a detected position of the cast metal strand from at least one of the sensors, and generating at least one control signal in response to the position signal such as, for example, a feed-forward control signal and/or a feedback control signal.
The control signals from the computer-based apparatus may be used to control a desired correcting device, such as a mold taper of a casting mold of the slab caster. U.S. patent application Ser. No. 11/627,511 filed on Jan. 26, 2007 is incorporated herein by reference in its entirety, and describes methods and devices for controlling mold face position in a continuous slab caster. Alternatively or in addition, the control signals from the computer-based apparatus may be used to control roll force or pressure profile of the withdrawal straightener, tilt of the withdrawal straightener, tilt of a set of pinch rolls, cooling spray onto rolls adjacent the slab caster, drive speed of a set of pinch rolls, and drive speed of the withdrawal straightener. In an embodiment, the computer-based apparatus further may include a database management system (DBMS) electrically interfacing to the programmable logic controller (PLC) and capable of storing position data received from the programmable logic controller (PLC), and where the position data is generated by the programmable logic controller (PLC) from the position signals received from the sensors.
A method for continuously casting steel slabs is also disclosed comprising the steps of:                assembling a continuous metal slab caster having a vertically-oriented casting mold, a withdrawal straightener positioned downstream of the casting mold, and a cutting tool positioned downstream of the withdrawal straightener,        assembling a first pair of position-detecting sensors adjacent entry to the withdrawal straightener and positioned to detect substantially laterally with respect to a direction of casting,        assembling a second pair of position-detecting sensors adjacent exit from the withdrawal straightener and positioned to detect substantially laterally with respect to the direction of casting,        assembling a third pair of position-detecting sensors adjacent exit from the cutting tool and positioned to detect substantially laterally with respect to the direction of casting,        assembling a computer-based system electrically connected to the sensors,        introducing molten metal into the casting mold and casting a metal strand downwardly from the casting mold, through the withdrawal straightener, and through the cutting tool,        monitoring substantially lateral positions of the cast strand using the first, second, and third pairs of sensors as casting proceeds, and        electronically storing the monitored positions as associated data in the computer-based system and using the associated data to actuate at least one correcting device capable of adjusting the orientation of the strand during casting.        
The associated data may then be processed using the computer-based system to generate at least one control signal (e.g., a feed-forward control signal and/or a feedback control signal). The control signals may be used to control the correcting device, which may be one or more of a mold taper of the casting mold, roll force or pressure profile of the withdrawal straightener, tilt of the withdrawal straightener, tilt of a set of pinch rolls, cooling spray onto rolls or strand adjacent the slab caster, drive speed of a set of pinch rolls, and drive speed of the withdrawal straightener.
As an option, a fourth position-detecting sensor may be assembled adjacent the withdrawal straightener, and optionally adjacent at least one set of pinch rolls, to detect the elevation of the strand along the direction of travel of the cast metal strand. The fourth position-detecting sensor may monitor an elevation position of the cast strand by detecting an elevation location of a first broad side of the cast strand as casting proceeds. The fourth position-detecting sensor detects the position of the cast strand substantially orthogonally to the position of the strand detected by the first, second and third lateral position-detecting sensors.
Monitoring of each of the first, second and third lateral positions may be accomplished by detecting a first lateral location of a first narrow side of the cast metal strand and a second lateral location of a second opposite narrow side of the cast metal strand. Again, in an embodiment the position-detecting sensors may comprise laser-based sensors, but, other types of position-detecting sensors may be used as desired in a particular embodiment.
Additionally, a slab caster plant is disclosed for producing continuously cast slabs with improved quality by monitoring and controlled positioning. The slab caster plant comprises:                (a) a vertically-oriented casting mold,        (b) optionally, a set of pinch rolls positioned downstream of the casting mold,        (c) a withdrawal straightener positioned downstream of casting mold, and if present, the set of pinch rolls,        (d) a cutting tool positioned downstream of the withdrawal straightener,        (e) a first pair of position-detecting sensors positioned adjacent entry to the withdrawal straightener and arranged to detect substantially laterally with respect to a direction of casting,        (f) a second pair of position-detecting sensors positioned adjacent exit from the withdrawal straightener and arranged to detect substantially laterally with respect to the direction of casting,        (g) a third pair of position-detecting sensors positioned adjacent exit from the cutting tool and arranged to detect substantially laterally with respect to the direction of casting, and        (h) a computer-based system electrically connected to each of the first, second and third position-detecting sensors and capable of controlling at least one correction device to modify orientation of the cast strand along the direction of travel.        
In an embodiment, the position-detecting sensors comprise laser-based sensors, or other type of position-detecting sensor in accordance with the desired embodiment.
As an option, the caster plant may further include a fourth position-detecting sensor positioned adjacent the withdrawal straightener and optionally a set of pinch rolls. The fourth position-detecting sensor is positioned to detect the position of the cast strand along the direction of travel through the slab caster plant substantially orthogonal to the position of the strand detected by at least one of the first pair, second pair or third pair of sensors.
The computer-based platform may include a programmable logic controller (PLC) and a database management system (DBMS). The PLC may be capable of being programmed with automation software and of receiving information (data/signals) indicating the detected position of a cast metal strand traveling through the caster plant at at least one of the first pair, second pair or third pair sensors, and generating at least one control signal such as, for example, a feed-forward control signal and/or a feedback control signal in response to the information. Furthermore, the PLC may be capable of receiving information (data/signals) indicating a detected position of a cast metal strand traveling through the caster plant from at least one of the first pair, second pair or third pair sensors, and transmitting the information to the DBMS. The DBMS is capable of storing the information and associating the information with other information received from other sensors. Also, the PLC is capable of receiving data, corresponding to a detected position of a cast metal strand traveling through the caster plant of at least one of the first pair, second pair or third pair from the DBMS, and processing the data to generate at least one control signal such as, for example, a feed-forward control signal and/or a feedback control signal.
The control signals may be used to control a correcting device capable of adjusting the orientation of the strand during casting. This adjustment in orientation is lateral to the direction of travel, but may also be elevational to the direction of travel of the cast strand, and/or rotational to correct for twisting of the strand during casting. The correcting device may be, for example, a mold taper position of the casting mold, roll force or pressure profile of the withdrawal straightener, tilt of the withdrawal straightener, tilt of a set of pinch rolls, cooling sprays onto to the strand adjacent the slab caster, drive speed of a set of pinch rolls, and drive speed of the withdrawal straightener.
These and other advantages and features, as well as details of illustrated embodiments of the disclosure will be more fully understood from the following description and drawings. Further limitations and disadvantages of particular embodiments will also become apparent to one of skill in the art, through comparison of such systems and methods with the embodiments as set forth in the remainder of the present application with reference to the drawings.